Bwog fell asleep at 8pm on Thanksgiving (and last night….oops), and was determined to find out why. Assuming those after-meal droopy eyes had something to do with science (the idea of a god of food comas was dismissed after much discussion), we set Bwogsleuth Zach Kagan on the trail. Here he presents a roundup of internet wisdom to reveal the cause of post-turkey sleep disorder.

It’s a familiar scene. You’re watching Thanksgiving day football, and your eyes start to droop. But it’s not just you—your whole family, aunts and cousins, that neighbor you only see three times a year—they’re all slouching in their chairs, lazily fighting the sweet embrace of sleep. Just then your Auntie Nora pipes up and says: “It’s the tryptophan! In the turkey!”

Ah! But you, seeker of truth, are just as much trapped in the cave as Auntie Nora, because the whole tryptophan in turkey causing drowsiness is but a myth. Pervasive myth at that: there’s even a Seinfeld episode where Jerry sedates his girlfriend with a big turkey dinner so he can play with her toys (it’s less creepy in context…well, on second thought it isn’t really). The truth is that that tryptophan is a mild sedative contained in turkey, but the story is a bit more complicated. It’s time to put your biochemistry caps on: tryptophan is an essential amino acid that you get from food. Your body needs it to make important stuff like boring ol’ vitamin B, but also fun neurotransmitters like serotonin and melatonin which calm you down and can make you drowsy. Case closed right? You eat lots of turkey, get ingest oodles of tryptophan, your brain goes into a serotonin producing overdrive, and you nod off to sleep halfway through Alcibiades’s speech.

If only it were that simple! There are a bunch of other amino acids in turkey as well, and tryptophan is one of the scarcer ones. Amino acids need to compete to get past the blood-brain barrier and on Thanksgiving there’s just too much competition and tryptophan gets drowned out. Really, the only way that tryptophan can make you drowsy is on an empty stomach, and how likely is that on turkey day? Turkey doesn’t even have a particularly high amount of tryptophan (both beef and soybeans contain more). So, what really makes you sleepy after Thanksgiving? The same thing that makes you sleepy after any meal.

It’s the brain’s response to a full belly. The fuller, the sleepier, and on Thanksgiving it’s common to eat more in one meal than you would in an entire day. Blood has to go down to your stomach and digest all the food (fats are especially slow to digest), and that means there is less blood to share with your muscles, organs, and nervous system, making you feel sluggish and tired. Studies have also shown that stretching of the small intestine can cause sleepiness.

Some of you at this point are saying “of course Bwog, I already knew that tryptophan doesn’t really make you sleepy after Thanksgiving, so there.” Well, there’s one final caveat to this issue, and we’ve saved it for dessert. All the carbohydrates you gobbled down in the bread, mashed potatoes, and, yes, pumpkin pie, results in the release of insulin. Insulin absorbs amino acids, but it largely ignores tryptophan. That helps tryptophan cut in line across the blood-brain barrier and enter the brain, producing serotonin and melatonin and making you drowsy. So, in the end does tryptophan make you sleepy on Thanksgiving? Well, not directly. It’s part of it, but you’d be sleepy after any giant meal with lots of fats, carbohydrates—no turkey necessary.